Re: [5.6.0-rc2-next-20200218/powerpc] Boot failure on POWER9

* Michael Ellerman [off-list ref] [2020-03-13 21:48:06]:

Sachin Sant [off-list ref] writes:

quoted

quoted

The patch below might work. Sachin can you test this? I tried faking up
a system with a memoryless node zero but couldn't get it to even start
booting.

The patch did not help. The kernel crashed during
the boot with the same call trace.

BUG_ON() introduced with the patch was not triggered.

OK, that's weird.

I eventually managed to get a memoryless node going in sim, and it
appears to work there.

eg in dmesg:

  [    0.000000][    T0] numa:   NODE_DATA [mem 0x2000fffa2f80-0x2000fffa7fff]
  [    0.000000][    T0] numa:     NODE_DATA(0) on node 1
  [    0.000000][    T0] numa:   NODE_DATA [mem 0x2000fff9df00-0x2000fffa2f7f]
  ...
  [    0.000000][    T0] Early memory node ranges
  [    0.000000][    T0]   node   1: [mem 0x0000000000000000-0x00000000ffffffff]
  [    0.000000][    T0]   node   1: [mem 0x0000200000000000-0x00002000ffffffff]
  [    0.000000][    T0] Could not find start_pfn for node 0
  [    0.000000][    T0] Initmem setup node 0 [mem 0x0000000000000000-0x0000000000000000]
  [    0.000000][    T0] On node 0 totalpages: 0
  [    0.000000][    T0] Initmem setup node 1 [mem 0x0000000000000000-0x00002000ffffffff]
  [    0.000000][    T0] On node 1 totalpages: 131072
  
  # dmesg | grep set_numa
  [    0.000000][    T0] set_numa_mem: mem node for 0 = 1
  [    0.005654][    T0] set_numa_mem: mem node for 1 = 1

So is the problem more than just node zero having no memory?

The problem would happen with possible nodes which are not yet present. i.e
no cpus, no memory attached to those nodes.

Please look at
http://lore.kernel.org/lkml/20200312131438.GB3277@linux.vnet.ibm.com/t/#u (local)
for more details.

The summary being: pgdat/Node_Data for such nodes is not allocated. Hence
the node_present_pages(nid) called  where nid is a possible but not yet
present node fails. Currently node_present_pages(nid) and node_to_mem_node
don't seem to be equipped to handle possible but not present nodes.

cheers

-- 
Thanks and Regards
Srikar Dronamraju